Water-soluble pouch compositions are known in the art. These compositions are easy to dose, handle, transport and store. Recently, water-soluble pouches containing cleaning or fabric care compositions have become popular.
U.S. Pat. No. 5,132,036 and U.S. Pat. No. 5,160,654 describe laundry treatment products in the form of a single or multi-compartment sachet which may be water-soluble. U.S. Pat. No. 5,198,198 describes a water-soluble container containing a multiple use amount of, for example, a fabric treatment composition.
Usually the pouches are formed by placing two sheets of material together, heat-sealing three edges, filling and then heat-sealing the forth edge. However, this method has the draw back that it is relatively slow and expensive. This is particularly an issue for cleaning or fabric care pouches which must be produced quickly and cheaply. In addition, heat sealing does not provide a strong seal and the heat can damage the pouch material resulting in leakage of the contents. Also, with heat sealing it is very difficult to seal more than two films together.
An alternative method of sealing is known as solvent-welding. This involves applying solvent to the film material and forming a seal between the solvated film and another film. Solvent-welding has the advantage that can be done quickly, continuously and does not use as much energy as heat-sealing. An additional advantage of solvent-welding is that the seal actually strengthens after the seal is made. This is due to the gradual loss of solvent from the seal area after the welding process which causes the bond between the film material to become stronger.
WO-A-97/35539 describes a method of encapsulation involving solvent-welding wherein the solvent is water. Water is the most convenient solvent for water-soluble pouches being cheap and easily obtainable. However, water alone is difficult to use in such a process because it rapidly flows away from the area to be sealed. Another problem is that it is difficult to apply the water homogenously causing some areas of the film to be weakened while other are not sufficiently solvated. Furthermore, solvent welding using water often results in air bubbles in the seal which weaken the seals integrity. All this means that it is difficult to implement high speed production of pouches using water as the solvent.
It is an object of the present invention to provide a solvent-welding process for water-soluble films, and in particular for the production of water-soluble pouches, that avoids the problems of the prior art. The process of the present invention uses a solvent system that has a specified viscosity. The solvent of the present invention does not cause such damage to the film, is easier to apply uniformly and produces a strong, stable seal. Consequently, the resultant pouches show less leakage over time than prior art solvent-welded pouches. Furthermore, the present process allows high-speed production and can be operated continuously. In addition, the present process allows more than two films to be sealed together. Other objects and advantages shall become apparent as the description proceeds.